Problem: Expand.
Solution: $\begin{aligned} &\phantom{=}({d^2+3})(d^2+2d+1) \\\\ &={d^2}(d^2+2d+1){+3}(d^2+2d+1) \end{aligned}$ $\begin{aligned} &=d^4+2d^3+d^2+3d^2+6d+3 \\\\ &=d^4+2d^3+4d^2+6d+3 \end{aligned}$